1. Field of the Invention
This invention relates to an image forming apparatus such as an electrophotographic copying machine, a laser beam printer and the like, and more specifically to an image forming apparatus in which a toner image carried on an endless belt-like toner image carrying belt is transferred to a printing paper by means of a transfer facing roller provided inside the toner image carrying belt and caused to move along the printing paper.
1. Description of the Prior Art
Recently, as represented by laser beam printers, image forming apparatus employing a toner system have begun to widely spread that can form clear images with high resolution. Among such image forming apparatus employing a toner system, image forming apparatus of the type that a toner image carried on an endless toner image carrying belt is transferred to a printing paper by means of a transfer facing roller provided inside the toner image carrying belt and caused to move along the printing paper, are very suitable for the promotion of downsizing of the products from the viewpoint of the structures thereof.
As one structure out of them, description will be given below of a cross-transfer type image forming apparatus in which a toner image carrying belt caused to move in a direction perpendicular to the direction of conveyance of a printing paper is rubbed on the printing paper by means of a transfer facing roller so as to transfer a toner image little by little in each process.
FIG. 2 is a schematic view of a conventional cross-transfer type image forming apparatus, and FIG. 3 is a schematic perspective view of the conventional cross-transfer type image forming apparatus. In FIGS. 2 and 3, the reference numeral 1 denotes a toner image carrying member comprising a photosensitive belt; 2a and 2b, toner image carrying rollers; 3, a cleaning device; 4, a discharging device; 5, a charging device; 6, an exposing device; 7, a developing device; 8, a transfer facing roller; 9, a printing paper; and 10, a transfer plate, and the reference character A denotes a rotating direction of the toner image carrying member 1.
Arrangement, operation and so on of the image forming apparatus constructed as described above will be described.
As shown in FIG. 2, the charging device 5, the developing device 7, the cleaning device 3, the discharging device 4 and the like are disposed around the toner image carrying member 1 whose surface is coated with a layer of an organic photoconductive material. The exposing device for applying a laser beam is disposed above the toner image carrying member 1.
The toner image carrying member 1 is rotated in a direction meeting at right angles to the direction in which the printing paper 9 is conveyed so as to be electrically charged by the charging device 5 when passing by the latter. Then the exposing device 6 applies a laser beam 6a to selected portions of the thus-charged toner image carrying member 1 to thereby form an electrostatic latent image.
Toner 7a is rubbed on the portions of the toner image carrying member 1 corresponding to the thus-formed electrostatic latent image by means of a developing roller 7b so that a toner image 7c is caused to appear as a visible image successively on the toner image carrying member 1. Then, the transfer facing roller 8 is caused to move inside the toner image carrying member 1 in a direction perpendicular to the direction of conveyance of the printing paper 9 while pressing the toner image carrying member 1 against the printing paper 9. As a result, the toner image 7c is transferred to the printing paper 9 by the pressure produced between the transfer facing roller 8 and the transfer plate 10. Thereafter, the transfer facing roller 8 is returned to the stand-by position thereof following the same path reversely. In this way, the transfer facing roller is caused to move back and forth inside the toner image carrying member 1.
In the conventional cross-transfer type image forming apparatus described above, however, the toner image 7c on the toner image carrying member 1 is transferred to the printing paper 9 only by the pressure produced between the transfer facing roller 8 and the transfer plate 10 while the transfer facing roller 8 is moved in the direction perpendicular to the direction of conveyance of the printing paper 9, resulting in the problems that the toner may be partially left on the toner image carrying member 1 and that the toner transferred to the printing paper 9 may return to the toner image carrying member 1 again.